Method of attaching a carbide ring to a steel tube

ABSTRACT

THIS IS A METHOD OF ATTACHING A CARBIDE RING TO THE OUTSIDE OF A STEEL TUBE SUCH AS A VALVE STEM. IT OVERCOMES THE PROBLEM CAUSED BY THE DIFFERENCE IN THERMAL COEFFICIENT OF EXPANSION BETWEEN CARBIDE AND STEEL. IN THE PREFERRED EMBODIMENT OF THE METHOD EMPLOYED, MOLTEN BRAZING COMPOUND AT A HIGH TEMPERATURE, E.G., 1,700*F., IS MELTED IN THE CLEARANCE SPACE BETWEEN THE CARBIDE RING AND THE STEEL TUBE. THE CARBIDE RING IS ALLOWED TO COOL TO ABOUT 1,000*F. WHILE THE STEEL TUBE IS KEPT HOT TO ABOUT 1,500* F. BY APPLYING HEAT TO THE INSIDE. A STEEL PLUG IS THEN PLACED INSIDE THE STEEL TUBE ADJACENT THE CARBIDE RING. THIS STEEL PLUG HAS BEEN SIZED TO HAVE A DIAMETER, AT ROOM TEMPERATURE, EQUAL TO THAT OF THE INSIDE OF THE STEEL TUBE IN ITS EXPANDED POSITION AT 1,000*F. AFTER THE PLUG IS INSERTED, HEAT IS NO LONGER APPLIED AND THE CARBIDE RING CONTINUES TO SHRINK AND TO DISPLACE THE EXCESS SEMI-MOLTEN BRAZING COMPOUND. THE STEEL TUBE ALSO STARTS CONTRACTING UNTIL IT CONTACTS THE PLUG. THE PLUG WHICH WAS PUT INTO THE TUBE AT ROOM TEMPERATURE, E.G., 80*F., HAS HEAT TRANSFERRED TO IT FROM THE STEEL TUBE AND THE PLUG ITSELF STARTS TO INCREASE IN SIZE. THE STEEL TUBE WHEN IT CONTACTS THE PLUG WILL BE AT LEAST AT 1,000*F. AND IS SOFT ENOUGH TO YIELD EASILY. AS THE TEMPERATURE OF THE STEEL PLUG INCREASES, IT CONTINUES TO EXPAND AND CAUSES ADDITIONAL YIELDING OF THE STEEL TUBE WHICH YIELDS SUFFICIENTLY SO THAT WHEN IT AND THE CARBIDE RING COOL, THEY DO NOT SEPARATE.

June 1971 L. B. WILDER E L METHOD OF ATTACHING A CARBIDE RING To A STEELTUBE Filed Dec. so, 1968 FIG I n u g INVENTORS LAWRENCE B. WILDER RENICP. VINCENT ATTORNEY FIG.2

IL! k United States Patent O 3,585,710 METHOD OF ATTACHING A CARBIDERING TO A STEEL TUBE Lawrence B. Wilder and Renic P. Vincent, Tulsa,Okla., assignors to Pan American Petroleum Corporation, Tulsa, Okla.

Filed Dec. 30, 1968, Ser. No. 787,909 Int. Cl. B23k 31/02 U.S. Cl.29473.1 Claims ABSTRACT OF THE DISCLOSURE This is a method of attachinga carbide ring to the outside of a steel tube such as a valve stem. Itovercomes the problem caused by the difference in thermal coefficient ofexpansion between carbide and steel. In the preferred embodiment of themethod employed, molten brazing compound at a high temperature, e.g.,1,700 E, is melted in the clearance space between the carbide ring andthe steel tube. The carbide ring is allowed to cool to about 1,000" P.while the steel tube is kept hot to about 1,500 P. by applying heat tothe inside. A steel plug is then placed inside the steel tube adjacentthe carbide ring. This steel plug has been sized to have a diameter, atroom temperature, equal to that of the inside of the steel tube in itsexpanded position at 1,000 F. After the plug is inserted, heat is nolonger applied and the carbide ring continues to shrink and to displacethe excess semi-molten brazing compound. The steel tube also startscontracting until it contacts the plug. The plug which was put into thetube at room temperature, e.g., 80 F., has heat transferred to it fromthe steel tube and the plug itself starts to increase in size. The steeltube when it contacts the plug will be at least at l,000 F. and is softenough to yield easily. As the temperature of the steel plug increases,it continues to expand and causes additional yielding of the steel tubewhich yields sufiiciently so that when it and the carbide ring cool,they do not separate.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention isconcerned with a method of fastening carbide to steel. It isparticularly concerned with the fastening of a carbide ring to theoutside of a steel tube.

(2) Setting of the invention It has been very difiicult to fastencarbide rings to the outside of steel tubes. A common method ofattaching a carbide ring to the steel tube is to leave a clearance spacebetween the two and fill that with a molten brazing compound. Thissystem may be satisfactory if the service for which the assembly isintended is not severe. However, for hard service this method is not atall satisfactory as the attachment will not stand up. The source of themain problem is that the differences in thermal coefiicient of expansionbetween carbide and steel cause a separation of the brazing material asthe assembly cools.

Some success has been made in this as described in our US. Pat.3,372,464. However, that system is not always completely satisfactory.For example, in the method described in that patent, slots are providedin the end of the steel tube. It would be preferred that a better methodbe devised and especially one where it would not be necessary to cutslots.

SUMMARY OF THE INVENTION This is a method of attaching a carbide ring toa steel tube. A molten brazing compound is placed between the carbidering and the steel tube which, when cooled, is bonded to both the steeltube and the carbide ring. Means are provided to apply heat to theinside of the steel pipe While permitting the outer carbide ring tocool. As the carbide ring cools, it contracts. At the same time, meansare provided to force the hot steel tube to yield an amount sufficientto compensate for the otherwise decrease in diameter due to cooling overthat decrease in size of the carbide ring. Thus, there is not sufficientdifferential shrinkage to cause separation of the brazing material.

This process in one embodiment is accomplished, for example, by placinga brazing compound at about 1,700 F. between the carbide ring and thesteel tube. The outer carbide ring is allowed to cool to about 1,000 E,for example, while the steel tube is kept at about 1,500 F. by applyingheat to the inside of the tube. A properly sized steel plug is used toforce the inner steel plug to yield while it is still hot. This plug issized to have a diameter, at room temperature, e.g., 80 F., equal to theinside diameter of the steel tube at 1,000 E, which is sufficiently hotfor the steel to yield easily. After the plug is placed inside the tube,the assembly is permitted to cool. The carbide ring continues to shrinkand the steel tube contracts until it contacts the plug. The transfer ofheat to the plug causes it to expand. This in turn causes the steel tubeto yield. Upon final cooling of the assembly, the steel tube decreasesin size about the same amount as, or slightly less than,

Various objects and a better understanding of the invention can be hadfrom the following discussion taken in conjunction with the drawings inwhich:

FIG. 1 is a cross sectional view of the end of a steel tube with thecarbide ring.

FIG. 2 illustrates a drawing of the steel plug which is to be insertedinto the steel tube of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is directed to FIG. 1which shows a steel tube 10 and a carbide ring 12 which is to beattached to the outer wall of the tube 10. Shown between tube 10 andcarbide ring 12 is a brazing compound 14. Care should be taken sothatthe brazing compound is evenly distributed about the tube. FIG. 2illustrates a steel plug and is indicated by reference numeral 16. Thefunction of the a plug will be explained subsequently. The plug 16 ispreferably solid steel having approximately the same coefficient ofthermal expansion as does tube 10. Plug 16 has three portions: a headportion 18, a tapered lead portion 20 and a center portion 22. Therelationship of the dimension of portion 22 to the steel tube 10 will bediscussed hereinafter.

3 Various sizes of the steel and carbide parts are indicated in thedrawing and are labeled as follows:

D is the bore diameter of the steel tube;

D is the outside diameter of the steel tube where the carbide ring isattached;

D is the bore of the carbide ring;

D is the diameter of section 22 of the steel plug;

L is the length of the section of the steel tube where the attachment isto be made;

L is a corresponding part of the plug and L=L The thickness of the wallof the tube at the point where the carbide ring 12 is to be attached isone-half the difference between 03 and D The difference between D and Dis determined by the required strength of the tube. The radial clearancebetween the carbide ring 12 and the tube is one-half the differencebetween D and D The difference in these diameters is determined by therequired radial clearance space for the brazing compound selected. Thisis ordinarily between about 0.062" and 0.093". Each of these diametersbecome larger as heat is applied and become smaller as they cool. Theproblem is that they change at a different rate. For example, thethermal coefficient of expansion for a carbide ring may be 3.5)(10- andfor steel it may be 7.85 10- for the expected temperature range.

Since upon cooling the steel tube shrinks at a faster rate than does thecarbide ring, the annular space containing the molten brazing materialexpands, thus requiring more material to be added if the space is to bemaintained full. It is not believed that this increase in volume offersany problem as long as the brazing material is in liquid form. However,after the brazing material starts to solidify, it becomes porous and, infact, separates from the carbide ring and the steel tube when roomtemperature is reached. In fact, 'we have often found that no bondbetween the brazing compound and the carbide ring or the steel tuberemains after it is cooled.

We have found a system whereby this annular volume or space between thecarbide ring and the steel tube can be made to decrease in volume as theassembly cools. Therefore, the brazing material becomes more dense as itis compressed in the annular volume rather than more porous as is thecase if the volume increases in size. The process and the means by whichthe natural physical properties of the materials are used to accomplishthis are described below.

The process of this invention has been successfully used to attach acarbide ring such as ring 12 to a steel tube such as tube 10. Thebrazing material used is identified as All-State 11, which iscommercially available. All surfaces to be attached by brazing, such asthe inner surface of the carbide ring 12 and the mating outer surface 15of the steel tube 10, are first covered with a suitable flux. Then thecarbide ring 12, while resting on shoulder 13 of the steel tube, iscentered over tube 10. The assembly is in an upright position asindicated in the drawing. By way of explanation, in one successfulapplication, the assembly was heated to l,700 F. and the molten brazingmaterial was flowed into place in the annular volume or space betweenthe carbide ring 12 and the steel tube 10. At this time heat is appliedto the interior portion of tube 10 adjacent the carbide ring by any wellknown means such as by an oxygen acetylene' torch, not shown. At thistime no heat is applied to the carbide ring 12 from the outside, but itis allowed to cool.

Heat is continued to be applied to the inside of the steel tube untilequilibrium heat flow from the inside of the tube to the carbide ring isreached. The heat applied to the inside of the tube is that necessary tokeep the brazing material between the tube 10 and the carbide ring 12semi-molten. 'One way this condition can easily be checked is byapplying a brazing rod (of the same material as the semi-molten brazingmaterial) at frequent time intervals to the semimolten brazing material.The temperature should be just high enough so that the new brazing rodmelts. At this temperature the brazing compound in the space between thering 12 and tube 10 is in the semi-molten stage. This test is possiblebecause the brazing material used has a remelt temperature which is someto 50 F. higher than that for the first melt. This process allows thecarbide ring to shrink to its minimum diameter consistent with theaverage temperature. Some of the brazing material will be displaced dueto the reduced annular space which was caused by cooling of the carbidering While maintaining the steel tube at a higher temperature, e.g.,l,500- F.

At this stage of the process, the heat source for the interior of thetube 10 is removed and the cylindrical surface 22 of plug 16 insertedadjacent the carbide ring 12. Cylindrical surface 22 has been machinedso that its diameter D is equal to the diameter of the bore of tube 10at a temperature at which the steel stem will still yield easily. Asuitable temperature is about 1,000 to 1,200 F.

As no heat is being applied to tube 10 now, tube 10 will continue toshrink and will contact surface 22 of plug 16. Heat from the assemblyflowing through the steel plug causes its diameter D to expand. Thisexpansion causes the bore of tube 10 to be expanded. As carbide ring12'is also reduced in diameter, this causes a reduction in the annularvolume for the brazing material 14. The carbide ring 12 continues tocool and its diameter D decreases, but the plug 16 continues to expanddue to its increased temperature resulting from the heat flow from theassembly to the plug. As the plug expands, the tube 10 being at anelevated temperature state yields easily and its diameter is thereforeincreased. This yield is substantially nonreversible. These actionscontinue until the plug has reached its maximum temperature anddiameter.

After this latter equilibrium temperature is reached, the plug startscooling and will decrease in diameter. However the steel tube has beenforced to yield and will not decrease in diameter, or at least only to avery limited degree, so that there is no appreciable increase in thesize of the annular volume occupied by the brazing'material. The steeltube has a diameter D after cooling which will remain at about the samesize as it was when it was at 1,200 E, or whatever the temperature waswhen heating equilibrium was reached. The plug 16, on the other hand,after it cools, i.e., to about 80 R, will have decreased its diametersufficiently so that it can easily be removed. The use of the processjust described resulted in a method of fastening a carbide ring to asteel tube which has been found to be permanent. Such an assembly hasgreat deal of detail, various modifications can be made therefromwithout departing from the spirit of the inventron.

What we claim is: i

1. A method of attaching a carbide ring to the outside of a steel tubewhich comprises:

placing said carbide ring around said steel tube;

placing a molten brazing compound in the clearance between said ring andsaid tube; I allowing the carbide ring to cool relative to thetemperature of the steel tube while maintaining said steel tube at atemperature at which it yields easily; forcing said steel tube to yieldradially to have an enlarged diameter; and permitting the assembly tocool to ambient temperature.

2. A method as defined in claim 1 in which heat is applied to the innerpart of said steel tube after the placing of the brazing compound tomaintain the tube at about 1,500 F. while permitting the carbide ring tocool to about 1,000 F. v

3. A method as defined in claim 1 in which said step of forcing saidsteel tube to yield includes placing a steel plug into said steel tube,which plug at ambient temperature has a diameter equal to the insidediameter of the steel tube when it is at the lowest temperature at whichit yields easily.

4. A method of fastening a carbide ring to the outside of a steel tubewhich comprises the steps of:

placing said ring around said tube; placing a molten brazing compoundbetween said ring and said tube; permitting the carbide ring to cool toa temperature between about 1,000 F. and 1,200 F. while applying heat tothe inside of said tube to keep it at about 1,500 F.; placing a steelplug which is cool with respect to the tube, into said tube, said plughaving a diameter when cool equal to that of the inside of the steeltube at 1,000 E; permitting the assembly to cool and thereafter removingthe steel plug. 5. A method of attaching a carbide ring to an unslottedsteel tube which comprises:

centering the steel tube within the carbide ring to form an annularspace;

placing a molten brazing compound in said space;

reducing the volume of said space while allowing said carbide ring, saidbrazing compound and said steel tube to cool by permanently increasingthe diameter of said steel tube.

References Cited UNITED STATES PATENTS 1/1922 Lewis 29447X 12/ 1932Everett 29447UX 10/ 1956 ODonnell 29447 8/1962 Sheinhartz et al 29447X1/ 1967 Stuart 29447X 3/1968 Reid et a1. 29447 3/ 1968 Vincent et a129-473.1 5/1968 Bari-oil et a1. 29447 JOHN F. CAMPBELL, Primary Examiner20 R. J. SHORE, Assistant Examiner US. Cl. X.R.

